Can the number of neutrons for an element ever differ?

Absolutely. An element is defined by the number of protons in the atomic nucleus. For example, any nucleus with a single proton is by definition hydrogen. There are, however, three different forms of hydrogen; the kind with no neutrons (which is the most usual form), one neutron (known as deuterium) and two neutrons (known as tritium). Every element has isotopes with varying numbers of neutrons.